Interferons (IFNs) are a well known family of cytokines secreted by a large variety of eukaryotic cells upon exposure to various stimuli. The interferons have been classified by their chemical and biological characteristics into four groups: IFN-α. (leukocytes), IFN-β (fibroblasts), IFN-γ (lymphocytes), and IFN-ω (leukocytes). IFN-α and β are known as Type I interferons: IFN-γ is known as a Type-II or immune interferon. The IFNs exhibit anti-viral, immunoregulatory, and antiproliferative activity. The clinical potential of interferons has been recognized.
Human leulcocyte interferon was first discovered and prepared in the form of very crude fractions by Isaacs and Lindenmann. Efforts to purify and characterize the material have led to the preparation of relatively homogeneous leukocyte interferons derived from normal or leukemic (chronic myelogenous leukemia or “CML”) donor leukocytes. These interferons are a family of proteins characterized by a potent ability to confer a virus-resistant state in their target cells. In addition, interferon can inhibit cell proliferation, modulate immune responses and alter expression of proteins. These properties have prompted the clinical use of leukocyte interferon as a therapeutic agent for the treatment of viral infections and malignancies.
During the past several decades a large number of human and animal interferons have been produced, identified, purified and cloned. Several of the interferon preparations have been prepared for clinical trial in both crude form, for some of the original interferon preparations, as well as in purified form. Several individual recombinant interferon-α species have been cloned and expressed. The proteins have then been purified by various procedures and formulated for clinical use in a variety of formulations. Most of the interferons in clinical use that have been approved by various regulatory agencies throughout the world are mixtures or individual species of human α interferon (Hu-IFN-α). In some countries Hu-IFN-β and γ have also been approved for clinical trial and in some cases approved for therapeutic use. The major thesis underlying clinical use of these interferons was that they were natural molecules produced by normal individuals. Indeed, the specific thesis was that all the interferons prepared for clinical use, be they natural-or recombinant-generated products, represented interferons that were produced naturally by normal people. This is true for a large number of interferons as well as specific growth factors, lymphokines, cytokines, hormones, clotting factors and other proteins that have been produced.